LAARS Mighty Therm VW-PW (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 14)

LAARS Heating Systems
Page 14
valve is directed to an open drain and protected
from freezing.
2. Install a properly sized thermal expansion tank on
the cold water supply line.
2.6.7 Pressure Relief Valve
The pressure relief valve must be installed in the
tapped opening provided in the boiler header with its
outlet piped to a drain or floor sink. Special attention
must be given to relief valve settings in installations
where the boiler is located on the ground floor of a tall
building, or where the operating temperature of the
boiler is above 210°F. In both instances, the static
pressure of the system is elevated, and could cause the
relief valve to leak. Where no special setting of the
relief valve is ordered, the factory will furnish a
125 psi setting.
WARNING
Hot water can scald! Hot water can produce
third degree burns in 6 seconds at 140°F (60°C) and
in 30 seconds at 130°F (54°C).
2.6.8 Water Pressure
Keep the water pressure in the system above
30 psi (207 kPa). If the system pressure drops below
30 psi (207 kPa), it could damage the heater through
lack of circulation. If for any reason, the water is
turned off temporarily, to service the equipment for
example, airlock could be a problem when the heater
is turned back on. To eliminate the airlock, open the
pressure relief valve (see Figure 23) and allow the air
to bleed out until water starts to flow. As soon as full
circulation is restored, the trapped air will be released
through the hot water faucets.
2.6.9 Pump Installation (Model VW)
1. Install a properly sized pump to provide water
circulation between the heater and the storage tank.
2. Size the pump to avoid an excessive temperature
rise (see Table 4), and to provide the correct flow
for prevailing water hardness conditions.
3. Install the pump in a cool location. The life of the
pump can be shortened by exposure to excessive
heat. If the pump is equipped with a thermal
protection device, excessive heat may trip the
thermal switch. This could cause the pump to
shut down intermittently, resulting in rapid
scaling of the heat exchanger.
4. If designed for floor mounting, install pump
securely on concrete block or pad at least
6 inches (152 mm) above floor level. This will
prevent flooding of the motor when the floor is
washed.
5. Do not suspend floor mounted pumps from piping.
6. Plumb piping to avoid putting strain on the pump
casing.
2.6.5 Pump Requirements
The VW heater does not have a factory installed
pump (see Table 4 for pump performance require-
ments). The PW heater does have a factory installed
pump which is for heater-to-tank circulation only.
VW and PW heaters are not designed for applica-
tions where the temperature of the water flowing
through the heater remains below the dew point, 110°F
(43°C).
If low inlet water temperatures are expected,
bypass plumbing as shown in Figure 20 should be used
to temper the incoming water.
The factory provided pump on the PW heaters,
and the pumps recommended for field installation on
VW heaters, are sized to provide proper circulation
through the heater, and through the heater-to-tank
circulation loop (see Figures 20 through 22).
If the heater-to-tank circulation loop does not
contain more than 6 elbows or 30 feet (9.1 m) of pipe,
the minimum pipe fitting should be 1-1/2 inches (38
mm). If the loop does contain more than 6 elbows or
30 feet (9.1 m) of pipe, the minimum size should be
2 inches (51 mm).
2.6.6 Pressure Buildup in Water System
The water utility supply meter may contain a
check valve, back flow preventer, or water pressure
reducing valve that will create a closed water supply
system. Contact the water supplier or local plumbing
inspector on how to control this situation.
Figure 23. Pressure relief valve.
During the heating cycle of the heater, the water
expands creating a pressure buildup in the water
system. The pressure relief valve may discharge hot
water under these conditions, causing a loss/waste of
energy and a buildup of lime on the relief valve seat.
NOTE: Do not plug the relief valve.
There are two methods to prevent the relief valve
from discharging hot water in a closed water system:
1. Install a pressure relief valve on the cold water
supply line. Make sure that the discharge of this